1. Technical Field
The application relates to a method and apparatus for use in measuring the penetration of military gas masks (respirators), filters and filter media by test aerosols, and more particularly to an optical device which employs polarized light for measuring the size spread parameter .sigma.g of the test aerosol used in the penetration measurements of said devices.
Sigma (.sigma.) is defined, in basic statistics texts e.g., as the standard deviation of a statistical distribution, in this case of aerosol particle sizes; the subscript ".sub.g " indicates that aerosol particle size here follows a natural geometric-shaped, standard distribution.
2. Description of the Prior Art
Methods and apparatuses in accordance with the prior art are known to exhibit certain shortcomings and problems which have existed at least since World War II, but the technology has its beginnings in mask testing in the World War II era and before. Among the systems of the prior art is a polarimeter system known as the "OWL", developed at about the time of World War II. This system provided for the testing of gas masks by oil droplet smokes which were size-characterized by measurements of the polarization of the light scattered by the oil droplets. It was attempted to obtain uniformly sized droplets of 0.3 .mu.m for mask testing, and to verify average droplet size continuously using the "OWL" system. The .sigma.g was not measured.
More recently, an updated polarimeter system utilizing newer technology, including a laser light source, has been developed. However, the new system has stability problems and, in addition cannot resolve the geometric standard deviation, .sigma.g, of the test aerosol size distribution for values of more than about 1.2. However, such narrow distributions are difficult to produce. Therefore it is desirable to measure and resolve .sigma.g for cases greater than 1.2. Ability to measure and resolve .sigma.g up to about 1.5 would be most useful since particle size distributions with this value are achievable and common through thermal generation using liquids, such as dioctyl phthalate (DOP).